This invention relates to circularly polarized antennas, and more particularly, to circularly polarized antennas for use in FM radio or in television broadcasting where the antennas are mounted to the sides of a support mast capable of supporting other antenna systems for other stations and channels. This invention, more particularly, relates to an antenna which when mounted on this mast radiates an omnidirectional pattern about the mast. The problem becomes increasingly difficult when the desired pattern about the tower is in the circularly polarized mode. In the circularly polarized mode, the pattern in both the horizontally and vertically polarized fields should approximate each other with the appropriate phase difference to achieve the desired circular polarization.
Although horizontally polarized television broadcasting has been almost exclusively used in the United States of America, it appears from recent test results that circularly broadcasting might greatly improve television reception in large metropolitan areas. For this reason, the F.C.C. (Federal Communications Commission) has recently approved the use of circular polarization in television broadcasting.
A circularly polarized antenna system using a combination of turnstile and vertical dipole radiators was patented by Ben-Dov (U.S. Pat. No. 3,943,522, issued Mar. 9, 1976). Although this antenna system provides circular polarization when several such antenna systems are stacked one above the other to achieve more gain in the broadside direction, it was found that the vertical dipole radiators alone when mounted on a single pole without the horizontal supports (for example supports 58 and 59 in FIG. 6) produced a substantial amount of radiation parallel to the axis of the pole. It is also desirable that the antenna be more compact and that the elements be able to be spaced closer to each other without destroying the proper phase relationships required between the vertical dipoles and the horizontal radiators.